The bomber targeted a tribal elder and a local police chief at a wedding in Nagarhar province, local government spokesman Attaullah Khugyani said.
It is not yet clear why the attack was carried out or how old the minor was.
Taliban spokesman Zabiullah Mojahid denied responsibility for the attack in a message to media on Friday.
The United States has been in on-again, off-again peace talks with the Taliban for months but the development is the first time Afghans have made an agreement of this nature.
And it comes after weeks of direct talks between the Taliban and the US about the terms and pace of a troop withdrawal. The Taliban always insisted direct talks with the Americans must come first, and Washington has until recently resisted.